Gaesten f



(Model.)

C 1'. JESPERSEN.

Surveying Instrument.

No. 231,325. Paten'd Aug. 17,1880..

UNiTi-:D STATES PATENT OFFICEo OARSTEN F. JESPERSEN, OF OOPENHAGEN, DENMARK.

SURVEYING-INSTRUMENT.

SPECIFICATION forming' part of Letters Patent No. 231,325, dated August 1'7, 1880.

Application filed May 8, 1880.

To all whom it may concem:

Be itknown that I, OARsrEN FRs J ESPER- SEN, of the city of Copenhagen, in the Kingdom of Denmark, have invented a certain new and useful Improvement in Instruments fo1` Layiug Out Circle Ourves or Arches in the Field in Civil Engineering; and I do hereby declare that the following is a full, clear, and eXact description thereoffwhich will enable others skilled in the art to which it appertains to make and use the same, reference being had to the aecompanying drawings, which form a part of this specifieation.

My invention relates to the art of civil engineering, and has for its object to faeilitate the marking out of curve-lines of any desired radius in the field-in the construction of railroads, for example; and it consists in the construction of a very simple, inexpensive, and convenient instrument adapted for this purpose, substantially as hereinafter more fully set forth.

In the annexed drawings, Figure 1 is a diagram rcpresenting the method of using the instrument which I call a curve-mirror, and of which Fig. 2 is a perspective view; Fig. 3, a side elevation, and Fig. 4 a top plan.

Similar letters of reference indicate corresponding parts in all the figures.

My invention is founded upon the axiom that in a circle of any given radius all angles constructed`upon a` chord in the circle with their point or apex resting in the periphery at any desired point therein, and having the chord for their base, are of equal size. To illustrate: All angles the sides of which intersect the circle at the points L N, (see Fig. l of the drawings,) where the chord intersects or cuts the periphery of the circle, and the points of which are in the periphery, as at M, (referring to the obtuse angle L M N will be an gles of equal degrees and, again, the angles formed at each end of the chord L N by tangents K O or O D to the circle-arch and its chord L N are not only of equal size, but of exaetly the same size or degrees as the angles constructed upon said chord. In other words, KLNzLMNzzLND.

It follows that if two mirrors which are adjustable in relation to each other are placed one perpendicularly above the other at any (Model.) V

given point in the circle-arc-for example, at the point marked M-aud are then adjusted in such a manner that one of the mirrors shall reflect a stake or any other mark placed at the point L, where the chord L N intersects the periphery, while the other mirror is so adjusted upon its vertical'axis or pivot that a stake placed at the opposite end N of the chord is reflected therein perpendicularly below (or above, as the case may be) the reflected figure in the first mirror, then the Vertical planes represented by the two mirrors will be at an angle to each other which is exactly one-half of the angles L M N or K L N or L N D, and that without regard to at what point in the are the mirrors so adjusted respective of each other are placed. Itis obvious, therefore, that after the proper adjustment of the mirrors in respect of the points (stakes) K L N or L N D is effected the arc of the circle can readily be marked in the field by staking out any (lesired number of points, as indicated by the reflections in the mirrors.

The apparatus itself is represented iu Figs. 2, 3, and 4 on the accompanying drawings, and is composed, it will be seen, of two small mirrors, A B, of rectaugular shape, which are mounted one vertically above the other upon a'post, O, having a thimble, 0', at its lower end, by means of which it`may be attached to the top of a stake, G2, of any suitable height.

The lowermost mirror, A, is h-inged, at c, upon a plate, E, upon which it may be adjusted by means of a set-screw, f, and spring g, as shown in Fig34, the back plate, E, being fixed rigidly upon post O. The upper mirror, B, on

the contrary, is pivoted upon the post or standard O, upon which it may be fixed in any given position by the set-scre w 70. This arrangement admits of the mirrors being placed at any de` sired angle to each other, the stake O2 being driven into the groundat M, for exampleso that the stationary mirror A will reflect the stake driven at L, after which the upper mirror, B, is turned until it refiects the stake driven at N. The mirrors are then further adjusted by turning the upper mirror until the reflected pictures of stakes L and N fall in the same Vertical line, to facilitate w-hich adjustment and cause it to be made with micrometrical nicety and exactness the plane of the IOO lower mirror maybe adj usted by means of the set-serew f.

This instrument or apparatus is used as follows: Two points are selected arbitrarily in the line of the are or curve to be marked out. The mirrors A I; are then adjusted at the proper angle and the movable mirror B fastened upon post U by its set-serew, after which the stake or standard G2 is driven into the ground at one of these points, M, and a stake is driven at the other point, L. Stake (32 is now turned until one of its mirrors, A, refleets the stake at L, when another stake is carried, at au equal distance from stake C2, to a point where the other mirror, B, will refleet it, at which pointN it is driven into the ground. Thus we have the angle L M N eiearly marked out, and by now substituting a plain stake for Cz at M and shifting C2, with its inirrors to the point N, adjusting it so that the mirror A will refieet the stake at M, another stake is planted equidistant from G2 at N, at the point farther down the are, where it, is refleeted in mirror B, and so on, the mirror-stake being shifted from point to point, making' a series of sueeessive staked points, through which the eurve is run.

lt is obvious that the relative axrangement of the mirrors may he reversed, if desired, the upper mirror being made stationary and the lower pivoted, without deviatin g' from the spirit of my invention, or that both the mirrors may be pivoted upon post C and provided with setscrews k for seeuring them in their adjusted positions. Henee I do not limit myself to the preeise construction herein shown and deseribed; hut

I claim as my invention and desire to secure by Letters Patent of the United States- 1. An apparatus or implement for the marking out or staking oi' eurve-lines iu the field, eomposed, essentially, of two plane mirrors, A B, mounted one above the other upon avertieal staff or post, C, and adjustable upon said post in respect of eaeh other, substantially as and for the purpose herein shown and set forth.

2. The apparatus or implement for marking out orstaking eurve-lines in the field, com posed of a stake, C2, having at its upper end a post or standard, (J, upon whieh is mounted rigidly the reetangularplate E, provided with a hinged adjustable mirror, A, set-serew f, and spring g, and also the pivoted mirror B, provided with the set-screw k, snbstantially as and for the purpose herein shown and speeitied.

In testimony whereof I have signed my name to the t'oregoing speeifioation in the presenee of two suhseribing' witnesses.

CARSTEN FRS JESPERSEN.

Wituesses:

FREDERIK WOLFF, CHARLES ERLANDSEN. 

